Changed my URL, now my site is gone!

So the person I am building my site for asked to me change the URL to the site. I am currently working with a multistie setup. http://arizona-stem-collaborative.org/ is the main site and http://arizona-stem-collaborative.org/unconference/ is the second site. I went into the sites setting and changed the url of the second site from /unconference to /21centerystem. It obviously didn’t work. So I tried changing it back and now nothing. If you go to it, it will take you to a page on the main site. When I trying going in to edit the /unconference site it just takes me to the main sites dashboard now.

I’ve looked in cPanel and don’t see /unconference as a subdomain anymore. the /unconference site database is still there, and if I dig deep enough into the main site FTP files I can find the images I had uploaded onto the /unconferece site.

So does anyone know of anything i can do to fix this? or do I have to start from scratch and rebuild this page.

Thanks.